https://www.avient.com/sites/default/files/2020-10/luxury-closures-gravi-tech-design-guide-2.0-application-specific.pdf
It is better to
fill out the part at slower speeds in-order to let
any compressed air escape, and to get the best
surface finish on the part.3
• Using all of the previous settings, record the
Transfer Pressure, Fill Time, and Injection
speed
• Reduce the injection velocity by 10% and
record the same values
• Keep reducing the injection velocity until a
fill time of 10-15 seconds is reached
Transfer
Pressure
(psi)
Fill
Time
(sec)
Injection
Velocity
(in/sec)
Relative
Shear Rate
Relative
Viscosity
1238 0 .20 8 .00 5 .00 247 .60
1125 0 .22 7 .00 4 .55 247 .50
1058 0 .25 6 .00 4 .00 264 .50
960 0 .35 5 .00 2 .86 336 .12
870 0 .45 4 .00 2 .22 391 .65
780 0 .58 3 .00 1 .72 452 .59
690 0 .85 2 .00 1 .18 586 .78
600 1 .35 1 .00 0 .74 810 .45
510 2 .50 0 .75 0 .40 1275 .83
420 5 .23 0 .50 0 .19 2198 .34
330 9 .56 0 .25 0 .10 3157 .99
240 15 .26 0 .10 0 .07 3667 .49
FIGURE 47 - Injection Speed
22 Gravi-Tech
• Calculate the Relative Viscosity for each of
the Injection Speeds using the equation
above (Transfer Pressure * Fill Time)
• Calculate the Relative Shear Rate for each
of the injection speeds using the equation
(1/Fill Time)
• Plot the points on a graph and find the
optimum velocity
• The optimum velocity will be where the
curve starts to level out
In figure 48 above, the optimum velocity is where
the plotted line crosses the black trend line;
therefore the optimum velocity would be about
1 .00 in/sec .
FIGURE 48 - The Injection Unit
Nozzle
Non-Return Valve Heater Bands Barrel
Screw
Hopper
Metering
Zone
Compression
Zone
Feed
Zone
FIGURE 47 - Non-Return Valve: Check Ring
Check Ring Open
Check Ring Closed
FIGURE 49 - The Injection Unit
FIGURE 50 - Non-return Valve: Check Ring
Design Guide 45
FIGURE 48 - Non-Return Valve: Ball Check
Ball Check Open
Ball Check Closed
Poppet Valve
The final type of non-return valve is called a
poppet valve .
End of Fill
Part Length
Dynamic Pressure
Hydrostatic Pressure
P
re
s
s
u
re
Gate End
Part
FIGURE 61 - Deflection Equations
H
F
WLMax Deflection:
0.002" (0.05mm)
1 =
W • H3
12
_______
bending =
F • L3
48 • E • I
_______
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
FIGURE 60 - Pressure vs Part Length
FIGURE 61 - Deflection equations
FIGURE 62 - For Plate Shaped Parts
FIGURE 63 - For Cylindrical Shaped Parts
Design Guide 49
• M
Moldings
= Combined mass of molded parts
• C
p
= Specific Heat of the material
Step 3 – Heat Removal Rate
• N
lines
= The total number of independent
cooling lines there are in the mold
• t
c
= The cooling time required by the part
(Determined in step 1)
Step 4 – Coolant Volumetric Flow Rate
• ΔT
Max,Coolant
= Change in coolant
Temperature During Molding (1°C)
• ρ
Coolant
= Density of coolant
• CP = Specific heat of coolant
Step 5 – Determine Cooling Line Diameter
• ρ
Coolant
= Density of coolant
• V
Coolant
= Volumetric flow rate of coolant
• μ
Coolant
= Viscosity of coolant
• ΔP
line
= Max pressure drop per line
(Usually equals half of the pump capacity)
• L
Line
= Length of the cooling lines
COOLING LINE SPACING
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
4
π
tc =
h2
1n
π2 • a
•
Tmelt – Tcoolant
Teject – Tcoolant
tc =
D2
1.61n
23.1 • a
Tmelt – Tcoolant
Teject – Tcoolant
a =
k
p * Cp
Qmoldings = mmoldings • Cp • Tme • Cplt – Teject
cooling
nlines
moldings
tccooling
Vcoolant
line
nmax, coolant • Pcoolant • Cp, coolant
Dmax =
4 • Pcoolant • Vcoolant
π • µcoolant • 4000
Dmin =
Pcoolant • Lline • V2coolant5
10π • ∆Pline
2D < H
line
< 5D
H
line
< W
line
< 2H
line
FIGURE 70 - Cooling Line Spacing
FIGURE 64 - Heat Transfer Equation
FIGURE 65 - Total Cooling for Mold
FIGURE 66 - Cooling Required by Each Line
FIGURE 68 - Max Diameter Equation
FIGURE 69 - Min Diameter Equation
FIGURE 67 - Volumetric Flow Rate Equation
50 Gravi-Tech
ADHESIVE ADVANTAGES DISADVANTAGES
Cyanoacrylate
Rapid, one-part process
Various viscosities
Can be paired with primers
for polyolefins
Poor strength
Low stress crack resistance
Low chemical resistance
Epoxy
High strength
Compatible with various
substrates
Tough
Requires mixing
Long cure time
Limited pot life
Exothermic
Hot Melt
Solvent-free
High adhesion
Different chemistries for
different substrates
High temp dispensing
Poor high temp performance
Poor metal adhesion
Light Curing Acrylic
Quick curing
One component
Good environmental resistance
Oxygen sensitive
Light source required
Limited curing configurations
Polyurethane
High cohesive strength
Impact and abrasion resistance
Poor high heat
performance
Requires mixing
Silicone
Room temp curing
Good adhesion
Flexible
Performs well in high temps
Low cohesive strength
Limited curing depth
Solvent sensitive
No-Mix Acrylic
Good peel strength
Fast cure
Adhesion to variety
of substrates
Strong odor
Exothermic
Limited cure depth
Design Guide 51
Bibliography
1 .